Documentation: Make explicit that env. variables replace all sonar.properties...

Documentation: Make explicit that env. variables replace all sonar.properties parameters for docker setups

* Update install-server.md

Add that environment replace replace sonar.properties parameters

* Update server/sonar-docs/src/pages/setup/install-server.md

Co-authored-by: Tobias Trabelsi <64127335+tobias-trabelsi-sonarsource@users.noreply.github.com>

Co-authored-by: Tobias Trabelsi <64127335+tobias-trabelsi-sonarsource@users.noreply.github.com>